Multilayered substrate

Abstract

A multilayered substrate comprises: an underlying substrate; and a gallium nitride layer epitaxially grown above the underlying substrate and comprising gallium nitride containing silicon; the gallium nitride layer having a top surface with a radius of 50 mm or more, the gallium nitride layer having a thickness of 4 μm or more, wherein a silicon concentration on the top surface of the gallium nitride layer has a distribution in which an outer circumferential silicon concentration at a radial position 10 mm from an edge of the top surface is higher than a central silicon concentration at a center of the top surface, the central silicon concentration is 4×1015 cm−3 or more and less than 2×1016 cm−3, and an outer circumferential silicon contamination concentration, which is an excess of the outer circumferential silicon concentration from the central silicon concentration, is 1.2×1015 cm−3 or less.

What is claimed is: 
     
         1 . A multilayered substrate, comprising:
 an underlying substrate; and
 a gallium nitride layer epitaxially grown above the underlying substrate and comprising gallium nitride containing silicon; 
 the gallium nitride layer having a top surface with a radius of 50 mm or more, 
 the gallium nitride layer having a thickness of 4 μm or more, 
 wherein a silicon concentration in the top surface of the gallium nitride layer has a distribution in which an outer circumferential silicon concentration at a radial position 10 mm from an edge of the top surface is higher than a central silicon concentration at a center of the top surface, 
 the central silicon concentration is 4×10 15  cm −3  or more and less than 2×10 16  cm −3 , and 
 an outer circumferential silicon contamination concentration, which is an excess of the outer circumferential silicon concentration from the central silicon concentration, is 1.2×10 15  cm −3  or less. 
   
     
     
         2 . The multilayered substrate according to  claim 1 , wherein in a circular region inside an annular region with a width of 20 mm from an edge of the top surface, the excess of the silicon concentration in the top surface of the gallium nitride layer from the central silicon concentration, is 0.4×10 15  cm −3  or less. 
     
     
         3 . The multilayered substrate according to  claim 1 , wherein the silicon concentration in the top surface of the gallium nitride layer has a distribution in which an intermediate silicon concentration at a radial position 30 mm from a center of the top surface is higher than the central silicon concentration and lower than the outer circumferential silicon concentration.